This research will examine host functions and their roles in M13 viral DNA replication, the physical and genetic properties of the origin of M13 DNA replication, DNA-protein interactions during viral DNA replication and properties of the M13 gene 2 protein. Bacterial mutants defective for DNA chain initiation or elongation and for the joining of Okazaki fragments will be studied with regard to possible defects in viral DNA replication. The origin of M13 DNA replication will be precisely mapped using restriction endonucleases. The unique termini at the site of discontinuity in RFII molecules will also be sequenced. Mutants in the M13 gene 2 will be located on individual restriction fragments from the gene 2 region, a portion of the viral chromosomes also containing the origin of DNA replication. An in vitro system will be developed for M13 RF yields SS synthesis and used for the assay and purification of the gene 2 protein. The purified gene 2 protein will be characterized with regard to its specificity and mechanism of action. The stage at which the M13 gene 3 protein associates with viral DNA will be determined. The physical properties of viral DNA-gene 5 protein complexes will be examined from cells infected with mutants defective in phage morphogenesis.